Resiliency Considerations; Limitations And Restrictions - Cisco MDS 9000 series Configuration Manual

Limitations and Restrictions

S e n d d o c u m e n t a t i o n c o m m e n t s t o m d s f e e d b a c k - d o c @ c i s c o . c o m
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Resiliency Considerations

When you configure IOA, consider the following resiliency guidelines:
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Caution
Limitations and Restrictions
When you configure IOA, consider the following limitations:
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Cisco MDS 9000 Family I/O Accelerator Configuration Guide
3-8
Interconnect core switches in each site for optimal routing.
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Plan for Geneneration 2 and above line cards to avoid any FC-Redirect limitations. There is a limit
of only 32 targets per switch if Generation 1 modules are used to link the ISLs connecting the IOA
switch and target switches or if the host is directly connected to a Generation 1 module.
Depending on the WAN transport used, you may have to tune the Fibre Channel extended B2B
credits for the round-trip delay between the sites.
Plan to have a minimum of one additional IOA service engine for each site for handling IOA service
engine failures.
Tuning for E_D_TOV: Fibre Channel Error Detect Timeout Value (E_D_TOV) is used by Fibre
Channel drives to detect errors if any data packet in a sequence takes longer than the specified
timeout value. The default timeout value for E_D_TOV is 2 seconds. IOA has an built-in reliability
protocol (LRTP) to detect and recover from ISL failures by doing the necessary retransmissions.
However, you need to ensure that it recovers before the expiry of E_D_TOV. LRTP is not required
if the FCP-2 sequence level error-recovery procedures are enabled end-to-end (primarily in the tape
drivers) because this helps to recover from timeout issues.When the FCP-2 sequence level
error-recovery procedure is not enabled, you must tune certain timers in order to protect the site from
ISL failures.
Reduce the LRTP retransmit value from the default value of 2.5 seconds to 1.5 seconds. For
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more information, see the
If the ISLs are FCIP links, the FCIP links must be tuned in order to detect link flaps quickly. By
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default, FCIP links detect a link failure in 6 seconds based on TCP maximum retransmissions.
To reduce the time taken to detect failures, you need to set the maximum retransmission
attempts in the FCIP profile from the default value of 4 to 1.
Modifying the default setting to a lower value results in quick link failure detections. You must
make sure that this is appropriate for your deployment. We recommend that you modify the
default setting only for those applications which are sensitive to E_D_TOV values. For other
applications, the default configuration is sufficient.
Only 512 flows are supported when IOA and IVR co-exists.
You can provision only one intelligent application on a single service engine. In SSN-16 there are 4
service engines and each service engine can host a single intelligent application.
In Cisco NX-OS Release 4.2(1), only IOA and FCIP can run on the same SSN-16 as in the following
example:
– If one of the service engines runs SME on an SSN-16, you cannot configure another application
the remaining service engines on this SSN-16.
"Setting the Tunable Parameters" section on page
Chapter 3 Deployment Considerations
4-16.
OL-20708-01, Cisco MDS NX-OS Release 5.0(1a)